Magnetic field monitor having automated quantitative calibration of magnetic field sensor

ABSTRACT

A magnetic field monitor includes a magnetic field sensor that generates an electronic signal at a time period representing a magnetic field of the environment and includes a sensor transducer having a sensor bobbin, a primary coil, a secondary, over-winding coil, a sensor circuit, a controller connected to the primary coil, and a digitally controlled potentiometer connected to the secondary coil and controller. A non-linear output is converted to a quantitative linear output.

FIELD OF THE INVENTION

The present invention relates to magnetic field sensors, and moreparticularly, this invention relates to calibration of magnetic fieldsensors.

BACKGROUND OF THE INVENTION

The output of magnetic field sensors vary, with their output based on avariety of factors, including temperature, tolerance variances in theelectronic control circuitry, and the sensor transducer orientationrelative to Earth's magnetic North. This may lead to processingchallenges that present themselves for many magnetic field sensors, butin particular, for multi-axis magnetic field sensors because each of thethree primary axes are oriented in different positions relative tomagnetic North, for example, in an X, Y and Z axis direction. As aresult, the output from magnetic field sensors may be non-linear, andthis type of non-linear output may be difficult to quantify. Inapplications where quantification is desired, advanced, complicated andexpensive electronic components and circuits are often required toprocess the signals and attempt to force the output of one or more ofthe magnetic field sensors to be calibrated to a reliable Tesla(magnetic measurement) value. Some existing solutions are limited toforcing a calibration over a very small bandwidth, and only undercertain conditions. Additionally, in cases where the magnetic fieldsensor is employed at a location where there is an excessive magneticfield, such as near rebar or other ferrous materials, the magnetic fieldsensors typically will not operate in a calibrated mode, since there isa bias to the output due to the environment.

SUMMARY OF THE INVENTION

This summary is provided to introduce a selection of concepts that arefurther described below in the Detailed Description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

A magnetic field monitor for monitoring magnetic field fluctuationsoccurring in an environment comprises a magnetic field sensor configuredto generate an electronic signal at a time period representing amagnetic field of the environment. The magnetic field sensor comprises asensor transducer having a sensor bobbin and a primary coil woundthereon and including first and second ends, and a secondary,over-winding coil including first and second ends, a sensor circuitconnected to the first end of the primary coil, a controller connectedto the second end of the primary coil, and a digitally controlledpotentiometer connected to the first end of the secondary coil andoperatively connected to the controller.

A self-calibrating module is connected to the magnetic field sensor andcomprises a calibrator connected to the magnetic field sensor andconfigured to generate a relative baseline signal based on an averagevalue of electronic signals generated at previous time periods torepresent the magnetic field of the environment, and a comparatorconnected to the calibrator and configured to determine a differencebetween the relative baseline signal and electronic signal and generatea calibrated output signal if the difference is greater than or equal toa threshold. When a calibrated output signal is not generated, thecontroller and digitally controlled potentiometer are configured tooperate the sensor transducer to obtain a quantitative linear output.

The digitally controlled potentiometer may be configured to sweep avoltage from negative to positive over the secondary, over-winding coiland provide a changing voltage to the secondary, over-winding coil,wherein each different voltage produces a current that changes theoutput frequency of the sensor transducer. A positive and a negative lowdrop-out (LDO) voltage regulator may be connected to the digitallycontrolled potentiometer. The secondary, over-winding coil may approachzero at the midpoint of the potentiometer voltage sweep.

An electronic ground may have a tolerance resistor and connected to thesecond end of the secondary, over-winding coil. The controller may beconfigured to generate a sensor response curve and convert a non-linearoutput of the sensor transducer to a quantitative linear output. Thecontroller may be configured to update a sampling rate of the magneticfield sensor.

The magnetic field sensor may comprise a multi-axis magnetic fieldsensor having primary axes oriented in different positions relative tomagnetic North and having a non-linear output channel at each axis. Thecontroller may comprise a counter, a signal processing circuit, a serialperipheral interface (SPI) connected to said digitally controlledpotentiometer and a universal asynchronous receiver-transmitter (UART)for software control. The magnetic field monitor may include a pluralityof magnetic field sensors, a calibrator connected to each of themagnetic field sensors and configured to generate the relative baselinesignal based on an average value of the electronic signals from each ofthe magnetic field sensors. A sensor input/output controller may beconnected to the self-calibrating module and have a signal combiner tocombine the electronic signals from the plurality of magnetic fieldsensors into a single electronic signal. A sensor event assessor may beconnected to the sensor input/output controller and configured toreceive and process the single electronic signal to provide assessmentinformation about a sensed event.

In yet another example, a magnetic field monitor monitors magnetic fieldfluctuations occurring in an environment and comprises a magnetic fieldsensor configured to generate an electronic signal at a time periodrepresenting a magnetic field of the environment. The magnetic fieldsensor may comprise a sensor transducer having a sensor bobbin, aprimary coil wound on the sensor bobbin, the primary coil having firstand second ends, a secondary, over-winding coil wound over the primarycoil, said secondary, over-winding coil including first and second ends,and a sensor circuit connected to the first end of the primary coil, acontroller connected to the second end of the primary coil, and adigitally controlled potentiometer connected to the first end of thesecondary, over-winding coil and operatively connected to thecontroller.

A positive and a negative voltage source may be connected to thedigitally controlled potentiometer. The digitally controlledpotentiometer may be configured to sweep a voltage from negative topositive over the secondary, over-winding coil and provide a changingvoltage to the secondary, over-winding coil. Each different voltageproduces a current that changes the output frequency of the sensortransducer. The controller may be configured to generate a sensorresponse curve and convert a non-linear output of the sensor transducerto a quantitative linear output.

In yet another aspect, a method of monitoring magnetic fieldfluctuations occurring in an environment may comprise providing amagnetic field sensor that includes a sensor transducer having a sensorbobbin, a primary coil wound on the sensor bobbin, the primary coilhaving first and second ends, a secondary, over-winding coil wound overthe primary coil, said secondary, over-winding coil including first andsecond ends, a sensor circuit connected to the first end of the primarycoil, a controller connected to the second end of the primary coil, anda digitally controlled potentiometer connected to the first end of thesecondary, over-winding coil and operatively connected to thecontroller. The method includes sweeping a voltage from positive tonegative at the digitally controlled potentiometer and over thesecondary, over-winding coil to provide a changing negative to positivevoltage at the secondary, over-winding coil, wherein each differentvoltage produces a current that changes the output frequency of thesensor transducer to produce a non-linear output. The method furtherincludes generating at the controller a sensor response curve andconverting the non-linear output of the sensor transducer to aquantitative linear output.

DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome apparent from the Detailed Description of the invention whichfollows, when considered in light of the accompanying drawings in which:

FIG. 1 is a block diagram of a conventional magnetic field sensingsystem.

FIG. 2 is a block diagram of a magnetic field sensor used in themagnetic field sensing system of FIG. 1.

FIG. 3 is a block diagram of the input/output controller and sensorevent assessor shown in FIG. 1.

FIG. 4A is a block diagram of the magnetic field monitor in accordancewith a non-limiting example.

FIG. 4B is a block diagram similar to that of FIG. 4A and showing a flowsequence in operation of the magnetic field monitor.

FIG. 5 is a fragmentary block diagram showing components connected tothe primary coil and secondary, over-winding coil wound on the sensorbobbin in the magnetic field monitor of FIG. 4A.

FIG. 6 is a top plan view of the sensor bobbin of FIG. 5 without woundcoils thereon.

FIG. 7 is an isometric view of the carrier that holds sensor coils andsensor bobbin.

FIG. 8 is a fragmentary top plan view of the sensor carrier showing thesensor bobbin and wound sensor coils.

FIG. 9 is an end view of the sensor carrier of FIG. 7.

FIG. 10 is a sectional view of the carrier of FIG. 8 taken along line10-10 of FIG. 8.

FIG. 11 is an isometric view of the sensor bobbin and wound sensor coilsreceived on the carrier support.

FIG. 12 is an isometric view of the sensor bobbin.

FIG. 13 is a front elevation view of the sensor bobbin.

FIG. 14 is a sectional view of the sensor bobbin taken along line 14-14of FIG. 13 showing the winding direction of the primary coil.

FIG. 15 is a sectional view of the sensor bobbin along line 15-15 ofFIG. 13 showing the winding direction of the secondary, over-windingcoil.

FIG. 16 is an exploded view of components from the sensor transducer,including the carrier components, sensor bobbin, primary coil, andsecondary, over-winding coil.

FIG. 17 is a graph showing the frequency response curve of potentiometersettings from “0” as −2.5 volts to setting 255 at +2.5 volts.

FIG. 18 is a graph showing the gain plot as a change in milliTesla perkilohertz change in the sensor calculated for each of three (X, Y and Z)axes from the sweep of the transducer over 256 settings.

DETAILED DESCRIPTION

Different embodiments will now be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsare shown. Many different forms can be set forth and describedembodiments should not be construed as limited to the embodiments setforth herein. Rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope to those skilled in the art.

The magnetic field monitor, in accordance with a non-limiting example,reliably and repeatedly allows the conversion of qualitative,uncalibrated, non-linear magnetic sensor output into quantitative Teslacalibrated linear output over a wide bandwidth range. The magnetic fieldmonitor not only provides a rapid technique for calibration, butaccounts for differences in outputs based on sensor orientation relativeto magnetic North.

The magnetic field monitor will monitor magnetic field fluctuationsoccurring in an environment and may be incorporated within aself-calibrating module such as described in commonly assigned U.S. Pat.No. 10,165,228, the disclosure which is hereby incorporated by referencein its entirety. For example, when a calibrated output signal is notgenerated using the system as described in the '228 patent, the magneticfield monitor may be configured operate the sensor transducer to obtaina quantitative linear output.

For purposes of explanation, a short description of the sensor eventassessor training and integration as described in '228 patent is setforth relative to FIGS. 1-3 and further reference should be made to thedescription in the '228 patent to understand fully the workings andoperation of that system. The present magnetic field monitor may be usedwith that dynamically self-adjusting system as described in the '228patent and commonly assigned U.S. Pat. Nos. 9,354,291 and 10,107,872,the disclosures which are hereby incorporated by reference in theirentirety.

With reference to FIG. 1, a block diagram 100 of a sensor event assessorsystem as described in the incorporated by reference '228 patent isshown. As illustrated, FIG. 1 includes an environment 105, at least twomagnetic field sensors 110 which provide output signals 115A and 115Bover the connection 120. Output signals 115A, 115B are received byinput/output (I/O) controller 145, which receives the multi-channeloutput signals 115A and 115B and combines them into a single channel 115that is passed to sensor event assessor 150. Although two output signals115A and 115B are shown, the technology is not limited to only twosensors, but a large plurality of sensors may be used. In this exampleand relative to the description, the sensors 110 are magnetic fieldsensors.

In general, the environment 105 may be natural or built and is usuallydescribed using a combination of atmosphere, climate and weatherconditions. Example, environments may include, but are not limited to,desert, tundra, canopy, jungle, riverine, aquatic, littoral, savannah,marine, urban or the like.

In one embodiment, the environment 105 is a localized area or portion ofan environment, similar to an ecosystem. For example, in one embodimentthe area represented by environment 105 may approximate the range ofoperation of magnetic field sensors 110.

In one embodiment, environment 105 may be an outdoor area. However, inanother embodiment, environment 105 may be an indoor area such as aroom, a structure or the like. In yet another embodiment, environment105 may be a combination of indoor and outdoor areas such as an outpost,or the like. Additionally, part or all of environment 105 may be dry,partially or completely submerged, partially or completely buried, andthe like. Further details are described in the incorporated by reference'228 patent.

With reference now to FIG. 2, a block diagram 200 of one of the at leasttwo magnetic field sensors 110 as a magnetic field monitor, in thisexample, is shown in accordance with one embodiment. The magnetic fieldsensor 110 may include magnetic field sensor 220, calibration module240, and instant comparator 210. The magnetic field monitor alsoincludes an optional block comparator 230 and accelerometer 225.Magnetic field sensor 220 may be a flux gate magnetometer sensor, asuper conducting quantitative interference detector (SQUID), a magnetoresistive sensor, spin electron relaxation frame (SERF) sensor or thelike.

Magnetic field sensor 220 may sample environment 105 periodically at apre-defined rate of time and generates a corresponding signal 130 foreach sampling period. For example, the magnetic field sensor 220 may usea 1 MHz crystal to establish a nanosecond sample rate. The magneticfield sensor 220 outputs a signal 130 to instant comparator 210,calibration module 240 and optional block comparator 230.

The calibration module 240 may receive an output signal 130 frommagnetic field sensor 220 and generate a relative baseline signal 280.For example, after the calibration module 240 receives an initial timeperiods worth of signals 130, the calibration module 240 may average thesignals 130 and generate a relative baseline signal 280. In other words,the relative baseline signal 280 is similar to a calibration,recalibration, zero or baseline for the particular environment 105 beingmonitored. In one example, the relative baseline signal 280 may be arelative value and not an explicit magnetic field strength value.

The instant comparator 210 may perform a comparison between the signal130 and relative baseline signal 280 to recognize a change inenvironment 105. When the resultant difference between the magneticfield of the environment 105 and relative baseline signal 280 is greaterthan or equal to a pre-defined difference threshold, the instantcomparator 210 provides an output signal 115.

The instant comparator 210 in an example may not use an actual magneticfield strength value as the threshold value, but may instead use athreshold value related to the difference between the signal 130 and therelative baseline signal 280. Thus, in an example, neither the signal130 nor the relative baseline signal 280 need include a specific orquantified value for magnetic field 110 as long as the magnetic fieldsensor 220 provides a consistent representation of the magnetic field110 in the signal 130. However, in another embodiment, the signal 130and/or relative baseline signal 280 may include a specified valuerelated to the magnetic field 110.

For example, the threshold value may be based on the absolute value ofthe difference between the signal 130 and the relative baseline signal280. By using the absolute value of the difference, the instantcomparator 210 is well suited to recognizing changes in magnetic field110 that increase the field strength as well as changes in magneticfield 110 that reduce the field strength.

The optional block comparator 230 may operate in a manner similar to theinstant comparator 210, but may be calibrated to recognize changes inthe magnetic field 110 over a greater time period than the instantcomparator 210. When the change over time for the relative baselinesignal 280 is greater than or equal to a pre-defined threshold, theblock comparator 230 may provide an output signal 115. Further detailsof operation are described in the incorporated by reference '228 patent.

The optional accelerometer 225 may be used to provide motion andorientation information to the sensors 110. For example, if one or moreof the sensors 110 were hanging from a tree, rolled across the ground,bumped, rotated, moved or the like, the accelerometer 225 may provideorientation and motion information that would allow sensors 110 tomaintain its calibration. Further details of operation are described inthe incorporated by reference '228 patent.

With reference now to FIG. 3, a block diagram of an I/O controller 145and a sensor event assessor 150 is shown in accordance with an example.Although in this example, the I/O controller 145 is shown as distinctfrom the sensor event assessor 150, and in another example, the I/Ocontroller 145 may be located within a sensor event assessor 150.

In an example, the I/O controller 145 includes a multi-channel sensorinput 360, an electronic signal receiver 365, a signal combiner 368 anda single channel output 370. In yet another example, the multi-channelsensor input 360 provides two-way communication with the plurality ofsensors 110, each of the plurality of sensors 110 having its ownchannel, such as 115A and 115B. The electronic signal receiver 365 mayreceive electronic signals from one or more of the plurality of sensors110 at a pre-defined sample rate. The signal combiner 368 may bundle theelectronic signals from one or more of the plurality of sensors 110 intoa single electronic signal 115. The single channel output 370 mayprovide the single electronic signal 115 to the sensor event assessor150.

For example, the I/O controller 145 may receive the multi-channel outputsignals 115A and 115B and combines them into a single channel 115 thatis passed to sensor event assessor 150. Moreover, the I/O controller 145can also communicate with each of the sensors 110. For example, the I/Ocontroller 145 is capable of adjusting the sample rate of one or more ofthe sensors 110. In addition, the I/O controller 145 may adjust thepower consumption of one or more sensors 110. The I/O controller mayadditionally monitor, organize, cascade, utilize and otherwise interactwith each of the sensors 110.

In yet another example, the I/O controller 145 may also automaticallyadjust the baseline settings of one or more of the sensors 110 in thenetwork based on one or more other sensors 110. For example, if a roguesensor is providing an output signal that is outside of the normal (withrespect to other sensors 110 in the network), I/O controller 145 mayprovide a calibration update to the rogue sensor to the appropriatebaseline. In so doing, a network wide baseline or calibration can beautomatically achieved.

In yet another example, the sensor event assessor 150 may receive theoutput signal 115 from the I/O controller 145 and provide assessmentinformation 345 in a user accessible format. The sensor event assessor150 may include an event detection receiver 310, a filter module 320, anevaluation module 330 and a user recognizable output generator 340.Event detection receiver 310 receives an electronic output signal 115related to an event detected by sensors 110 as described in detail inFIGS. 1 and 2.

The filter module 320 may compare the electronic output signal 115 witha predetermined event detection threshold. In other words, theelectronic output signal 115 is passed through filter module 320 if theelectronic output signal 115 is greater than or equal to thepredetermined event detection threshold. The evaluation module 330 mayreceive the electronic signal from the filter module 320 and provideassessment information about the event. The assessment information maybe based on previously trained information stored in a database 335.User recognizable output generator 340 provides the assessmentinformation 345 about the event in a user recognizable format. Furtherdetails are described in the '228 patent. Other system information 390may be accessed and a database 335 store data as described in the '228patent.

Referring now to FIG. 4A, there is illustrated a block diagram of themagnetic field monitor 400 that has the automated quantitativecalibration and includes the major components of the magnetic fieldsensor circuit 402 that includes a power supply in this example, and isconfigured to generate an electronic signal at a time periodrepresenting a magnetic field of the environment. This magnetic fieldsensor 400 includes the sensor circuit 402 and a sensor coil 404, alsotermed a sensor transducer or sensor transducer assembly, that includesa sensor bobbin 406 (FIG. 6). As better shown in FIGS. 5 and 6, aprimary coil 410 is wound on the sensor bobbin 406 as an inner coil andincludes first and second ends 412, 414 and a secondary, over-windingcoil 420 is wound on the sensor bobbin 406 as an outer coil and includesfirst and second ends 422, 424. The sensor coil 404, or sensortransducer and sensor circuit 402, form a magnetic field sensor 405 thatis outlined by the dashed lines in FIG. 4A, although one or allcomponents could form the magnetic field sensor, such as thepotentiometer and other components described below. The sensor circuit402 is connected to the first end 412 of the primary coil 410 and acontroller 430 as a microcontroller (MCU) with an analog-to-digitalinput as an example is connected to the second end 414 of the primarycoil. A digitally controlled potentiometer 432 is connected to the firstend 422 of the secondary, over-winding coil 420 and operativelyconnected to the controller 430 as shown in FIG. 4A. The second end 424of the secondary, over-winding coil 420 is connected to ground 435 via aprecision 100 ohm resistor.

In an example, a self-calibrating module 240 and other components, suchas described relative to FIG. 2, may be connected to the magnetic fieldmonitor 400 and may calibrate as described with the circuits of FIGS.1-3. The calibration module 240 may be configured to generate a relativebaseline signal based on an average value of the electronic signalsgenerated at previous time periods to represent the magnetic field ofthe environment. The comparator 210 may calibrate and may be configuredto determine a difference between the relative baseline signal andelectronic signal and generate a calibrated output signal if thedifference is greater than or equal to the threshold. When a calibratedoutput signal is not generated, the controller 430 and digitallycontrolled potentiometer 432 may be configured to operate the sensortransducer 404 and other components to obtain a quantitative linearoutput.

The controller 430 may be configured to generate a sensor response curveas described later and convert a non-linear output of the sensortransducer or sensor coil 404 to a quantitative linear output. Aplurality of the magnetic field sensors 405 may be used and a calibrator240 connected to each of the magnetic field sensors and configured togenerate the relative baseline signal based on the average value of theelectronic signals from each of the magnetic field sensors. In anexample, the sensor input/output controller 145 (FIG. 3) may beconnected at the calibration module 240 and output signal 115 and have asignal combiner to combine the electronic signals from the plurality ofmagnetic field sensors into a single electronic signal. The sensor eventassessor 150 may be connected to the sensor input/output controller 145and configured to receive and process the single electronic signal toprovide assessment information about a sensed event.

The sensor bobbin 406 (FIG. 6), as will be described in greater detailbelow, includes a metglas core 436 that is received within a trough 438of the sensor bobbin. In an example, the digitally controlledpotentiometer 432 is an 8-bit digitally controlled potentiometer, forexample, an analog device number AD5254BUZ100, and is configured tosweep a voltage from negative to positive over the secondary,over-winding coil 420 and provide a changing voltage to the secondary,over-winding coil. Each different voltage produces a current thatchanges the output frequency of the sensor transducer assembly, orsensor coil 404. In an example as shown in FIG. 4A, a positivelow-dropout (LDO) voltage regulator 440 of about 2.5 volts may beconnected to the digitally controlled potentiometer 432 and a −2.5 voltsLDO voltage regulator 442 may be connected to the digitally controlledpotentiometer 432 to provide a sweep of voltage from −2.5 volts to +2.5volts.

As shown in FIG. 4A, the controller 430 may include a counter 446, asignal processing and input/output circuit 448, a serial peripheralinterface (SPI) 450 connected to the digitally controlled potentiometer432, and a universal asynchronous receiver-transmitter (UART)communications controller 452 that interoperates with software control454 that may include external software receive 456, which may beincluded and processed via a processor 457, which could be part of thecontroller 430 or separate. In an example, the counter may be a 16-bitcounter for analog-to-digital conversion, where the sensor output 411 isreceived from the sensor primary coil 410 and passed into the 16-bitcounter. The SPI controller 450 may help control operation of thedigitally controlled potentiometer 432. In an example, the controller430 could be a PIC24FJ 16-bit microcontroller. The different componentsmay be positioned on a sensor printed circuit board (PCB) 460 as anon-limiting example.

As will be explained in greater detail below, the voltage to thesecondary, over-winding coil 420 approaches zero at the midpoint of thedigitally controlled potentiometer 432 voltage sweep. The electronicground 435 includes a tolerance resistor, which in this example is a 100ohm resistor, and is connected to the second end 424 of the secondary,over-winding coil 420 (FIG. 5). The controller 430 may be configured toupdate a sampling rate of the magnetic field sensor 405, and in apreferred example, the magnetic field sensor comprises a multi-axismagnetic field sensor having primary axes oriented in differentpositions relative to magnetic North and having a non-linear outputchannel at each axis, which in an example, are three channels for the X,Y and Z-axes.

Referring again to FIG. 4A, the magnetic field sensor output 411 is afrequency, in kilohertz, and received at the controller 430. A knownvoltage moves through a known number of turns in the secondary,over-winding coil 420 through a specific resistance and allows a knownmagnetic field referring to the Bio-Savart Law as explained below. Atany given setting of the digitally controlled potentiometer 432, theknown magnetic field is able to be calculated. The digitally controlledpotentiometer 432 is controlled by the controller 430 and thepotentiometer in one example will provide a varying voltage in a linearfashion for each setting, from one supply of voltage at the “zero”setting, and the second supply voltage at the number 255 setting. Thesoftware, such as part of the controller or separate processor 457 forthe monitor 400, controls the controller 430 to start a setting zero,and the software logs the magnetic field.

The controller 430 receives the frequency output and communicates thevalue to the software, which logs this value of the magnetic field as afunction of frequency. The controller 430 (or other device) may includea database memory for storing such values. This process may be repeated255 more times for each potentiometer 432 setting to provide arelationship of the magnetic field to the frequency. The software aspart of the program and the controller 430 or other processor calculatesthe change in frequency per potentiometer setting to find the gain as achange per unit. The maximum gain is chosen by the software andcommunicates to the controller 430 to set the digitally controlledpotentiometer 432 to that value with the highest gain to operate in a“sweet spot,” as will be explained in greater detail in an examplebelow. The software chooses 20 positions (ten higher and ten lower) ofpotentiometer settings and uses the frequency response and the knownvalues of the magnetic fields at those settings to calculate a responsecurve. This response curve may be a six order polynomial fit over the 21(the 10 lower, the center point, and the 10 higher) potentiometersettings. When a calibration loop is complete, the polynomial fit actsas a transfer function to calculate the magnetic field in real time byconverting change in frequency to change in magnetic field.Post-calibration, the controller 430 outputs the measured frequencysensor value and the software converts it to a calibrated magnetic fieldvalue.

FIG. 4B illustrates an auto calibration flow sequence in a calibrationloop, where the magnetic field sensor output is a frequency as describedabove and the software operating with the controller 430 directs thecontroller 430 to set a potentiometer 432 value to a value “zero.” Themagnetic field sensor output for a sample is “0a” and themicrocontroller outputs 0a to the software and receives five samples:0a, 0b, 0c, 0d, and 0e. The software average is the five samples andlogs the sample 0ave as the zero average. This process is looped 250more times for the potentiometer setting 1, 2, 3 . . . 255. Loggedvalues from the 0ave to the average of the 255 settings (255ave) are fitto the 6th order polynomial equation and the delta frequency perpotentiometer change is calculated to find the maximum response (gain)of the sensor coil 404. The software instructs the controller 430 to setthe digitally controlled potentiometer 432 to a value with the maximumgain, which is also known as the “sweet spot.” The values for eachdiscrete value that are 10 values above and 10 values of thepotentiometer setting below the sweet spot are established and the 21potentiometer setting values are used to fit with the 6th orderpolynomial function. This polynomial fit becomes a translation functionand the software operating the controller 430 uses this function tocalculate the real-time magnetic values over the 21 potentiometerranges, also known as the bandwidth.

Referring now to FIGS. 7-11, there is illustrated generally a carrier470 for the sensor bobbin 406 and the sensor coils 410, 420, which arereceived over the sensor bobbin and its core 436 received in the trough438 (FIG. 6). The sensor coils 410, 420 are constructed using known coilwire and bonding, for example, NEMA MW 29-C with 36 PN bond, and thewound sensor bobbin 406 is received on a lower carrier support 472 thatreceives a carrier housing cover 474 and top plate 476. The end view(FIG. 9) shows the head or end 478 of the sensor bobbin 406 (known asthe bobbin head 478) and the sectional view (FIG. 10) shows the sensorbobbin 406, core 438 as a core ribbon, and sensor coils as the primarycoil 410 and secondary over-winding coil 420. As shown in FIG. 8, thecarrier support 472 includes four pins labeled PIN 1 to PIN4 forconnecting to the printed circuit board 460. In a non-limiting example,the carrier 470 may be about 20 millimeters in length (20.320 in oneexample) and about 5.7 by about 6.6 millimeters in cross-section. Thesensor bobbin 406 with the primary coil 410 and secondary over-windingcoil 420 wound thereon is received in the bottom surface of the carriersupport 472. The carrier support 472 includes the four pins that arenumbered PIN1 to PIN4 and have the respective ends of the coils 410, 420connected thereto. An example completed sensor bobbin 406 with woundcoils 410, 420 and received on the carrier support 472 is shown in FIG.11 with the bobbin heads 478 secured in the carrier support 472.

Referring now to FIG. 12, there is illustrated the sensor bobbin 406,which includes the enlarged rectangular configured ends as the bobbinheads 478. The sensor bobbin 406 may be about 18 millimeters long andincludes the trough 438 formed within the central portion and is about15 millimeters long in this example. The trough 438 may be about 0.5millimeters, and in an example, about 0.476 millimeters in depth byabout 0.8 millimeters, and in an example, 0.78 millimeters in width.These dimensions can vary. The core 436 is received within the trough438 of the sensor bobbin 406, such as by Loctite 401 adhesive as anon-limiting example. For example, about 0.001 milliliter of Loctite 401adhesive may be applied in the trough 438 and the core 436 inserted. Thecore 436 may be ribbon configured, in an example, and is inserted intothe trough 438 with the adhesive and is pressed down for about 20seconds to allow the Loctite 401 to cure for one minute.

Referring now to FIGS. 13-15, there are illustrated the front elevationview (FIG. 13) of the sensor bobbin 406, also termed coil formingbobbin, and in FIG. 14, the sectional view taken along line 14-14 ofFIG. 13 and showing the winding direction (W) for the primary coil 410and in FIG. 15, the sectional view along line 15-15 of FIG. 13 showingthe winding direction (W) for the secondary, over-winding coil 420. Theprimary coil 410 is the first coil that is wound. The process forwinding starts with a coil wire such as NEMA MW 29-C 36 PN bond to pinnumber 1 toward the end of the inner face of the bobbin head 478 at thesquare notch 480 (FIG. 12). The primary coil 410 is wound clockwise fromPIN1 in the direction of the arrow onto the coil forming sensor bobbin406, starting in contact with the inner face of the bobbin head 478. Inan example, four layers of 97 to about 100 turns per layer areaccomplished with each layer to be within about one turn of the firstlayer, ending at PIN4, which is the same end as PIN1. The layer of turnsis adjusted to fit between the ends. The bond point and four layers areshown in the primary coil 410 of FIG. 16, showing the end of the coilwith the stepped configuration, corresponding to the four layers.

For the secondary, over-winding coil 420, the coil wire is also madefrom NEMA MW 29-C 36 PN and the end wire is bonded to start the windingonto PIN2 at the end near the inner face of the bobbin head 478 and itis wound counter-clockwise from PIN2 and in the direction of the arrowas shown in FIG. 15 onto the sensor bobbin 406 and in contact with theinner face of the bobbin head and with the primary coil 410. Two layersof 97 to about 100 turns per layer may be wound with each layer to bewithin one turn of the first layer ending at PIN3, which is the same endas PIN2, and the layer turns are adjusted to fit between the ends. Anexample of the two layers is shown in the secondary coil of FIG. 16showing the stepped configuration.

Once the sensor bobbin 406 is wound, it is set within the carriersupport 472 (FIG. 11) and as shown in the exploded view of FIG. 16,which shows the carrier support, the upper carrier housing cover 474,and the top plate 476 and the primary coil 410 and secondaryover-winding coil 420. The sensor bobbin 406 is set within the carriersupport 472 and the inner, or primary coil 410 is soldered starting atits wire to PIN1 and ending the other wire at PIN4. The secondary,over-winding coil 420 as the outer coil is soldered starting with thewinding at PIN2 and end with the wiring at PIN3. It is possible to gluethe coil forming or sensor bobbin 406 with PIN1 marked upward from thecarrier support 472 into the center of the carrier with adhesive such asRTV734. The edges of the carrier housing cover 474 are glued to thecarrier support 472 with adhesive and the serial number label or topplate 476 is applied to the center of the top or carrier housing cover474.

The inner or primary coil 410 has about four layers of 97 to about 100turns per layer, with each layer within about one turn of the firstlayer. The secondary, over-winding coil 420 as the outer coil has abouttwo layers of 97 to about 100 turns per layer with each layer within oneturn of the first layer. The final assembly as shown in the carrier 470of FIG. 7 may be soldered onto the printed circuit board 460 with othercomponents as part of the magnetic field monitor 400. It is possible forthe magnetic field monitor 400 to be supported by a drone or othersupport structure on a drone.

A non-limiting example of the magnetic field monitor 400 uses a 400 turnsecondary, over-winding coil 420 placed over the sensor bobbin 406, alsotermed the transducer bobbin. However, it should be understood that adifferent number of turns may be used for the secondary, over-windingcoil 420. One end of the secondary, over-winding coil 420 may beattached to the electronic ground 435 through the precision 100 ohm,0.1% tolerance resistor. In this example, the second end 424 of thesecondary, over-winding coil 420 is attached to this ground resistor 435(FIG. 5). The first end 422 of the secondary, over-winding coil 420 isattached to a digitally controlled potentiometer 432, which is connectedto both the positive 2.5 volt and a negative 2.5 volt power source,which in this example, are the respective LDO regulators 440, 442. Theactual power sources 440, 442, both positive and negative, may haveother higher or lower voltage values if additional bandwidth isrequired. The digitally controlled potentiometer 432 in an example is8-bit potentiometer, although the magnetic field monitor 400 could beused with a 10, 12, 24- or any other resolution source. The 8-bitpotentiometer 432 has 256 different resistances, and as implemented, maybe scanned, swept or locked into any one of the resistance settings,from values 0 to 255. The digitally controlled potentiometer 432interfaces with the firmware-based controller 430 using an I2Cinterface. As is known, the I2C interface is a synchronous,multi-master, multi-slave, packet switched, single-ended serial computerinterface. The software control initiates a sweep of the voltage sourcesfrom the negative 2.5 volts at potentiometer setting zero (CO′) and asnoted by ohms law (voltage=current×resistance), provides a slowlychanging voltage supply to the secondary, over-winding coil 420,approaching 0 (zero) volts at the midpoint of the potentiometer sweep(position 128 on the 8-bit potentiometer) and continues up to thepositive 2.5 volts (position 255 on the 8-bit potentiometer).

Each different voltage that is provided to the secondary, over-windingcoil 420 produces a current (Ampere's Law), which changes the outputfrequency of the sensor transducer 404, i.e., the sensor coils. Thevalues of the non-linear frequency response of the scan/sweep for all256 supplied voltages (0.0195 volts per setting on the 8-bitpotentiometer, i.e., 5 volts divided by 256, is recorded by the softwarewithin a memory to obtain a sensor response curve, as shown in theexample graph of FIG. 17, which shows frequency response curve of asweep from potentiometer setting “0” (negative 2.5 volts) to setting 255(positive 2.5 volts). The lines numbered X, Y, and Z represent the threechannels for the X, Y and Z-axes. Each recorded potentiometer settingresponse is an average of five samples taken at 10 kHz (100 ms) samplerate. The sample rate may be slower or faster and the process will bethe same. As an example for Channel X in FIG. 17, on the upward sectionof the curve, A is the midpoint and high gain area, B is the upper 10thpotentiometer setting position and C is the lower 10th potentiometersetting, with D as the vertical height corresponding to the 6th orderfit between C and B where “normalized” operating hovers around D.

Using the Biot-Savart Law, the supplied current (I) length (a) andradius (r) of the secondary, outer winding coil 420 permits the systemto calculate a “Beta” (β) for the coil based on the permeability of thesensor transducer core 436 (μ0) and the turn-density, turns per inch(dl) per the below calculation (Biot-Savart):

$= {\oint{{\frac{\mu_{0}}{4\;\pi}\left\lbrack \frac{Idl}{r^{2} + a^{2}} \right\rbrack} \cdot \frac{a}{\sqrt{r^{2} + a^{2}}}}}$

The result is a constant value (“Beta” (β)) for that magnetic sensortransducer 404 that allows the calculation of the output voltage (0.0195volts per setting). Using Ohms Law (V=IR), in conjunction with theprecision 100 ohm resistor as ground 435 from the first end of thesecondary, over-winding coil 420 to ground, the system calculates thecurrent (I) per setting (β/100 Ohms=Current) to allow the calculation ofa precise value of Tesla, or more specifically, in an implemented case,milli-Tesla (mT), per setting on the digitally controlled potentiometer432. This step calculates the conversion of the non-linear response offrequency to the known mT value for that specific potentiometer setting.

Each resultant data point collected from the frequency scan is analyzedas a function of the change in mT (calculated from the change infrequency, the β and the 100 Ohm resistor) as a function of change infrequency per potentiometer setting. This provides a Gain plot of thechange in mT per (ΔmT/kHz) per potentiometer setting to determine whichpotentiometer setting results in the maximum amount of response/changein the sensor transducer. The graph in FIG. 18 shows an example plotthat is automatically derived from the sensor's Gain (ΔmT/kHz) as afunction of potentiometer setting where the Gain (change in milliTeslaper kilohertz change in the sensor) plot is calculated for each of thethree (X, Y and Z) axes from the sweep of the transducer over the 256settings from negative 2.5V to positive 2.5V using the resultantmilliTesla calculation that Biot-Savart equation provided. The highpoint of the curve for each of the X, Y and Z axes corresponds to the“sweet spot” and the high point of gain for each channel.

Once the Gain plot is calculated, the software automatically picks thepotentiometer setting where the Gain is at the maximum value for eachchannel independently. The three potentiometer values are set by themicroprocessor/software or controller 430 and locked into that value asa center point, or what may be referred to as the “sweet spot.” Thecontroller 430 and software then calculates the linearization of curvesurrounding the “sweet spot” by a 6th order polynomial-fit of the area.What area around the curve is polynomial-fit is a software-definedvariable of the amount of potentiometer settings adjacent to the “sweetspot.” The implemented case presently is 10 potentiometer settingshigher and 10 potentiometer settings lower. This number may be changeddepending on the desired bandwidth that is required. These polynomialfit calculations are stored in a configuration file within the memory,along with the other calculated values, including the “sweet spots,”lower and upper frequency bounds (defined by the 10 potentiometersettings above and below the sweet spot) and stored in a non-volatileformat. The polynomial fit acts as a translation function of thefrequency output of the magnetic sensor transducer 404 and the resultantvalue in quantified magnetic units (Tesla) over the software definedupper and lower frequency range.

This provides a quantitative output reading of the magnetic sensortransducer 404 (for each and all channels/axes individually) that areupdated at the sampling rate of the sensor network/system (asimplemented at 10 Hz/100 ms). If the environment changes such that thefrequency response of the sensors no longer fit the calculatedtranslation function, or if the frequency is outside of the upper andlower limits, the software automatically indicates that the sensortransducer(s) are out of calibration.

The low-dropout (LDO) regulators 440, 442 each may be a DC linearvoltage regulator, which may regulate the output voltage even when thesupply voltage is close to the output voltage. These devices haveadvantages over other DC to DC regulators because they have an absenceof switching noise and a smaller device size that is advantageous forthese types of sensors as described. It should be understood that otherhardware components may be used such as described relative to FIG. 5 inthe incorporated by reference '228 patent, and may include the operatingsystem, applications, different models and data that work with acomputer peripherals such as computer readable media, including one ormore processors, the computer usable memory such as ROM, or volatilememory, such as RAM, a data storage unit and signal generating andreceiving circuitry. These circuits may interoperate through a bus intoa display, an alpha-numeric input, a cursor control, differentinput/output devices, and communications interfaces.

Many modifications and other embodiments of the invention will come tothe mind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is understood that the invention is not to be limited tothe specific embodiments disclosed, and that modifications andembodiments are intended to be included within the scope of the appendedclaims.

That which is claimed is:
 1. A magnetic field monitor for monitoring magnetic field fluctuations occurring in an environment, comprising: a magnetic field sensor configured to generate an electronic signal at a time period representing a magnetic field of the environment, said magnetic field sensor comprising, a sensor transducer having a sensor bobbin and a primary coil wound thereon and including first and second ends, and a secondary, over-winding coil including first and second ends; a sensor circuit connected to the first end of the primary coil; a controller connected to the second end of the primary coil; and a digitally controlled potentiometer connected to the first end of the secondary coil and operatively connected to the controller; and a self-calibrating module connected to the magnetic field sensor, comprising, a calibrator connected to the magnetic field sensor and configured to generate a relative baseline signal based on an average value of electronic signals generated at previous time periods to represent the magnetic field of the environment; and a comparator connected to the calibrator and configured to determine a difference between the relative baseline signal and electronic signal and generate a calibrated output signal if the difference is greater than or equal to a threshold; and when a calibrated output signal is not generated, the controller and digitally controlled potentiometer are configured to operate the sensor transducer to obtain a quantitative linear output.
 2. The magnetic field monitor according to claim 1 wherein said digitally controlled potentiometer is configured to sweep a voltage from negative to positive over the secondary, over-winding coil and provide a changing voltage to the secondary, over-winding coil, wherein each different voltage produces a current that changes the output frequency of the sensor transducer.
 3. The magnetic field monitor according to claim 2 further comprising a positive and a negative low drop-out (LDO) voltage regulator connected to said digitally controlled potentiometer.
 4. The magnetic field monitor according to claim 2 wherein the voltage to the secondary, over-winding coil approaches zero at the midpoint of the potentiometer voltage sweep.
 5. The magnetic field monitor according to claim 1 comprising an electronic ground having a tolerance resistor and connected to the second end of the secondary, over-winding coil.
 6. The magnetic field monitor according to claim 1 wherein said controller is configured to generate a sensor response curve and convert a non-linear output of the sensor transducer to the quantitative linear output.
 7. The magnetic field monitor according to claim 1 wherein the controller is configured to update a sampling rate of the magnetic field sensor.
 8. The magnetic field monitor according to claim 1 wherein said magnetic field sensor comprises a multi-axis magnetic field sensor having primary axes oriented in different positions relative to magnetic North and having a non-linear output channel at each axis.
 9. The magnetic field monitor according to claim 1 wherein said controller comprises a counter, a signal processing circuit, a serial peripheral interface (SPI) connected to said digitally controlled potentiometer and a universal asynchronous receiver-transmitter (UART) for software control.
 10. The magnetic field monitor according to claim 1 further comprising a plurality of magnetic field sensors, a calibrator connected to each of the magnetic field sensors and configured to generate the relative baseline signal based on an average value of the electronic signals from each of the magnetic field sensors.
 11. The magnetic field monitor according to claim 10, comprising: a sensor input/output controller connected to said self-calibrating module and having a signal combiner to combine the electronic signals from the plurality of magnetic field sensors into a single electronic signal; and a sensor event assessor connected to the sensor input/output controller and configured to receive and process the single electronic signal to provide assessment information about a sensed event.
 12. A magnetic field monitor for monitoring magnetic field fluctuations occurring in an environment, comprising: a magnetic field sensor configured to generate an electronic signal at a time period representing a magnetic field of the environment and comprises: a sensor transducer having a sensor bobbin; a primary coil wound on the sensor bobbin, the primary coil having first and second ends; a secondary, over-winding coil wound over the primary coil, said secondary, over-winding coil including first and second ends; a sensor circuit connected to the first end of the primary coil; a controller connected to the second end of the primary coil; a digitally controlled potentiometer connected to the first end of the secondary, over-winding coil and operatively connected to the controller; and a positive and a negative voltage source connected to said digitally controlled potentiometer, wherein said digitally controlled potentiometer is configured to sweep a voltage from negative to positive over the secondary, over-winding coil and provide a changing voltage to the secondary, over-winding coil, wherein each different voltage produces a current that changes the output frequency of the sensor transducer, and wherein said controller is configured to generate a sensor response curve and convert a non-linear output of the sensor transducer to a quantitative linear output.
 13. The magnetic field monitor according to claim 12 wherein said positive and negative voltage source comprise a positive and negative low drop-out (LDO) voltage regulator connected to said digitally controlled potentiometer.
 14. The magnetic field monitor according to claim 12 wherein the voltage to the secondary, over-winding coil approaches zero at the midpoint of the potentiometer sweep.
 15. The magnetic field monitor according to claim 12 wherein the sweep of the voltage at said digitally controlled potentiometer is from about negative 2.5 volts to about positive 2.5 volts.
 16. The magnetic field monitor according to claim 12 comprising an electronic ground having a tolerance resistor and connected to the second end of the secondary, over-winding coil.
 17. The magnetic field monitor according to claim 12 wherein the controller is configured to update a sampling rate of the magnetic field sensor.
 18. The magnetic field monitor according to claim 12 further comprising a multi-axis magnetic field sensor unit having primary axes oriented in different positions relative to magnetic North and having a non-linear output channel at each axis.
 19. The magnetic field monitor according to claim 18 wherein the controller is configured to set the digitally controlled potentiometer having a gain at a maximum value for each channel independently.
 20. The magnetic field monitor according to claim 12 wherein said controller comprises a counter, a signal processing circuit, a serial peripheral interface (SPI) connected to said digitally controlled potentiometer and a universal asynchronous receiver-transmitter (UART) for software control.
 21. A method of monitoring magnetic field fluctuations occurring in an environment, comprising: providing a magnetic field sensor comprising a sensor transducer having a sensor bobbin, a primary coil wound on the sensor bobbin, the primary coil having first and second ends, a secondary, over-winding coil wound over the primary coil, said secondary, over-winding coil including first and second ends, a sensor circuit connected to the first end of the primary coil, a controller connected to the second end of the primary coil, and a digitally controlled potentiometer connected to the first end of the secondary, over-winding coil and operatively connected to the controller; sweeping a voltage from positive to negative at the digitally controlled potentiometer and over the secondary, over-winding coil to provide a changing negative to positive voltage at the secondary, over-winding coil, wherein each different voltage produces a current that changes the output frequency of the sensor transducer to produce a non-linear output; and generating at the controller a sensor response curve and converting the non-linear output of the sensor transducer to a quantitative linear output.
 22. The method according to claim 21 wherein the voltage to the secondary, over-winding coil approaches zero at the midpoint of the potentiometer voltage sweep.
 23. The method according to claim 21 wherein said magnetic field sensor comprises a multi-axis magnetic field sensor having primary axes, the method including orienting each axis in a different position relative to magnetic North and producing a non-linear output channel at each axis.
 24. The method according to claim 21 further comprising setting the potentiometer to have a gain at a maximum value for each channel independently. 